Computer networks are increasing in size and complexity. When only two workstations are in communication with each other, data transfer, synchronization, and a common language or data format is relatively simple to establish. When more than two workstations are connected, coordination, addressing, and identification problems become more complex. As the number of workstations increases, additional hardware is often needed. The hardware is used to coordinate the different requirements that need to be fulfilled in order for successful communication to take place.
One long-standing attempt at breaking up the complexities of networking is the OSI (open systems interconnection) Seven Layer Reference Model. This model represents a network as seven layers:
Application--Layer 7
Presentation--Layer 6
Session--Layer 5
Transport--Layer 4
Network--Layer 3
Datalink--Layer 2
Physical--Layer 1.
This seven layer model has become the de facto standard for networking; it segments functionality by layer and makes network construction more module with interchangeable parts. This model is widely referenced to the point that network managers refer to network problems as being a layer 3 (network layer) problem or a layer 2 (datalink layer) problem. Layer 3 and layer 2 are particularly important layers for determining overall network health; subsequently a network manager spends much of his time managing these layers.
When the number of workstations increases to above approximately 5, or especially 10, hardware is needed to manage all of the data traffic. All of the workstations are usually provided with a link to a hardware device known as a concentrator. The plurality of workstations communicate with the other plurality of workstations over these links and through the concentrator. One of the most basic functions of a concentrator is for the concentrator to function as a repeater.
Each workstation communicates by sending data in frames, where the frame has a destination MAC address. All network devices, such as those that allow a workstation to communicate over a network, are assigned a unique MAC address. The frame with the destination MAC address is sent from the workstation over a link to the repeater. A repeater takes the frame received on one link, and sends a frame out on all the other links. Each workstation connected to the repeater monitors its respective link, and when a frame arrives that has a destination MAC address that matches the workstations MAC address, the workstation reads the frame and processes the frame internally.
Once the number of workstations largely increases, for example beyond 100, or the amount of traffic through the concentrator becomes excessive, a concentrator including a switch, is used. Such a switch has more intelligence than a repeater. The switch looks at the destination address of each frame received on a link, and then based on information contained in the switch, the switch only forwards the frame onto the link, or links, where the destination MAC address exists. The switch can contain this information in a MAC address look-up table, and this look-up table can either be created by a system operator, or the switch can learn which MAC addresses are on a specific link, by reading source addresses on frames received over that specific link (build a look-up table). Other information, such as the quantity of frames received or transmitted onto a link, as well as the size, type and quality of frames can also be recorded by the switch. This information is stored as data in a database.
A repeater is usually used to group together a small number of workstations into what is often called a Local Area Network (LAN), with a switch connecting several LAN's. In this way, the number of workstations that are able to communicate with each other can be increased tremendously, without each frame having to be sent to each workstation. This cuts down on traffic and allows frames to be more quickly sent from one workstation to another.
Presently the number of workstations which are to be connected together, particularly in large companies with locations in many different cities, and several buildings in each of those cities, has caused the amount of traffic to overwhelm repeaters and switches. Therefore, higher level network coordination is required.
An Internet Protocol (IP) has been devised for coordinating such a large number of individual workstations, which often spread out in groups over a large geographical area. This Internet protocol uses an IP address in addition to the MAC address.
Routers are then provided which operate in a manner somewhat similar to switches, but instead read the IP address of a packet. Such a packet is formed of one or more frames. When a router receives a packet, it reads the IP address, and then based on internal information, forwards the packet to a specific port or ports. These ports are connected to links which can then either be connected to other routers in the network, or to, switches, repeaters or individual workstations depending on the how the router is configured.
A packet going from one workstation to another, may have to pass over links, and through several repeaters, switches and routers before it reaches its destination workstation. Also some packets may be destined for more than one workstation, as is often the case when multimedia is transmitted over a large network. The routers must contain information on the proper forwarding of packets, and this information must be updated. When a packet must pass through several routers, and when a workstation in one country wishes to communicate with a workstation several countries away, the packet is transferred from router to router through all of those countries.
Many large companies, have what is now known as Intranets. Intranets act much like the global Internet, but are limited to the workstations of a particular company spread out over many countries, cities and buildings in each city. Tools are needed which allow system operators to determine how to configure the routers and switches, and to identify problems which are causing the network to not operate properly.